Paper PS+AS+NS+SS-ThM11
Fabrication of Asymmetric Nanopores by Pulsed PECVD

Thursday, October 31, 2013, 11:20 am, Room 102 B

The field of nanopore fabrication has attracted a lot of attention recently due to their potential application in DNA sequencing, ionic field effect transistors, and detection and separation of biomolecules and nanoparticles. The objective of our research is to develop a simple approach for large area fabrication of nanopores (pore size ~ 1–10 nm) with atomic level precision. In this work, we first employ relatively large template structures (~ 100–250 nm) produced by track-etching or e-beam lithography. The pore size is then refined to the desired level by deposition of material using pulsed plasma enhanced chemical vapor deposition (PECVD). Pulsed PECVD has been developed as an alternative to atomic layer deposition (ALD) to deliver self-limiting growth of oxides like alumina and silica. Pulsed PECVD has two growth components that act sequentially: ALD-like growth during the plasma off step (γ ~ 0); and PVD-like growth during the plasma on step (γ ~ 1), where γ is the reactive sticking probability. The ALD contribution is constant at ~1 Å /pulse whereas the PECVD contribution can be typically varied from 0.5 - 5 Å/pulse by appropriate control of operating conditions. The degree of conformality in pulsed PECVD can be engineered by controlling the relative contribution of these 2 growth components. As such this technique can produce novel morphologies that are distinct from those produced by conventional deposition processes. We have developed feature scale models to predict the pore closure phenomenon in pulsed PECVD. This model successfully predicts experimentally observed profiles in features such as trenches and cylinders. The model findings will enable us to determine optimal operation conditions for obtaining the desired nanopore opening and geometry. Flux experiments on nanopore-based membranes are further employed to validate the feature scale models. Such well-defined nanopores can serve as an ideal platform for rigorous evaluation of hindered transport at the nanoscale.